1. Field of the Invention
This invention relates to a zoom lens used for the image pickup by a video camera, a film camera or the like.
2. Description of the Prior Art
A mechanical correction type zoom lens in which two independent lens groups are movable during zooming generally has two separate integral curves and effects zooming by the lens groups being moved along one of the integral curves. However, in a special zoom lens, for example, a zoom lens shown in Japanese Laid-open Patent Appln. No. 29658/1979 or Japanese Laid-open Patent Appln. No. 29659/1979, zooming is effected by causing said two integral curves to intersect each other and causing the lens group moved along one of the integral curves to change onto the other integral curve at the point of intersection between the integral curves.
In Japanese Laid-open Patent Appln. No. 28051/1980, in a mechanical correction type zoom lens which comprises, in succession from the object side to the image side, a first lens group for focusing, second, third and fourth lens groups movable for zooming and a fifth lens group as a relay lens and in which the second lens group and the fourth lens group are moved together during zooming, the following conditions are disclosed as the conditions under which the lens groups change from one integral curve onto the other integral curve during zooming: EQU .vertline..beta..sub.2 .multidot..beta..sub.4 .vertline.=.vertline..beta..sub.3 .vertline.=1 (1) ##EQU1## where .beta..sub.i is the lateral magnification of the ith lens group, Z is an equation which prescribes the zooming, x.sub.1 is the amount of movement of the second lens group and the fourth lens group during zooming, and x.sub.2 is the amount of movement of the third lens group during zooming.